Aqueous solutions containing significant concentrations of phosphorus and/or, nitrogen can cause significant problems if released into the environment. There are various sources for such solutions. These include sources such as leaching from landfill sites, runoff from agricultural land, effluent from various industrial processes, municipal wastewater, animal wastes such as wastewater from feedlots or other animal husbandry facilities and the like.
In such solutions, nitrogen is typically primarily present in the form of ammonia and phosphorus is typically primarily present in the form of phosphate. Many jurisdictions have laws which limit the permissible concentration of phosphorus and/or ammonia in treated wastewater discharged into the environment.
Various phosphorus removal and recovery technologies exist. Some of these technologies provide crystallization reactors. Conditions are maintained in the crystallization reactors which promote the crystallization of phosphate compounds. These include:    S. Regy et al. Phosphate recovery by struvite precipitation in a stirred reactor, LAGEP (March to December 2001) includes a survey of various attempts to remove phosphorus and nitrogen from wastewater by struvite precipitation.    Trentelman, U.S. Pat. No. 4,389,317 and Piekema et al., Phosphate Recovery by the Crystallization Process: Experience and Developments, paper presented at the 2nd International conference on Phosphate Recovery for Recycling from Sewage and animal Wastes, Noordwijkerhout, The Netherlands, Mar. 12-13, 2001, disclose a reactor and method for precipitating phosphate in the form of calcium phosphate, magnesium phosphate, magnesium ammonium phosphate or potassium magnesium phosphate.    Ueno et al., Three years experience on operating and selling recovered struvite from full scale plant (2001) Environmental Technology v. 22 p. 1373 disclose the use of sidestream crystallization reactors to remove phosphate in the form of magnesium ammonium phosphate (also known as struvite).    E. V. Munch et al., Making a business from struvite crystallization for wastewater treatment: turning waste into gold, paper presented at the 2nd International conference on Phosphate Recovery for Recycling from Sewage and animal Wastes, Noordwijkerhout, The Netherlands, Mar. 12-13, 2001, discloses the use of a struvite crystallization process for removing nitrogen and phosphorus from wastewater in the form of struvite.    S. A. Parsons et al., Assessing the potential for struvite recovery at sewage treatment works, (2001) Environmental Technology v. 22, p. 1279 survey various attempts to remove nitrogen and phosphorus from wastewater in the form of struvite.    Tsunekawa et al. Patent Abstracts of Japan No. 11-267665 discloses a reaction tower for removing phosphorus from water.
Struvite can be formed by the reaction:Mg2++NH4++PO43−+6H2O⇄MgNH4PO4.6H2OA benefit of removing phosphorus and nitrogen by producing struvite is that struvite can be recovered and has value as a slow-release fertilizer.
Some of the prior processes which have produced struvite from phosphates and ammonia in wastewater produce undesirably small particles of struvite. Such small particles have diminished value as fertilizer.
There remains a need for a cost-effective methods and apparatus for removing phosphorus, nitrogen and similar solutes from wastewater and other aqueous solutions.